This invention relates to solenoid actuated fuel injectors for engines and the like and, in particular, to a method of assembly that simplifies setting of the injector valve stroke.
A solenoid actuated fuel injector for automotive engines is required to operate with a small and precise stroke of its core or valve in order to provide a fuel flow rate within an established tolerance. In some current injectors, the stroke is adjusted at assembly by moving an adjustable valve seat a predetermined dimension from a valve seated position. This adjustment is made after sealing of joints in the fuel conducting elements has been performed, such as by crimping or penetration welding of a solenoid pole piece to a surrounding tubular valve guide. This allows the stroke setting operation to compensate for component movement or shrinkage, which are likely occurrences with crimped or welded joints. However, the requirement for an adjustable valve seat adds cost and complexity to the assembly process.
The present invention provides a pole piece or core stop that is welded to a guide tube after a stroke setting operation. A continuous penetration seam weld is used in order to provide a hermetic seal of the joint between the parts. The hermetic penetration seam weld does not tend to move the parts axially, or normal to the direction of weld penetration. However, such a seam weld does tend to shrink the outer tubular component, which can cause a shift in the preset valve stroke.
In accordance with the present invention, the stroke is set by adjusting the position of the pole piece or valve stop within an associated guide tube to obtain the desired valve stroke. The guide tube is then fixed to the valve stop in a manner that maintains the preset valve stroke. This is accomplished by first welding the guide tube to the pole piece or valve stop by a series of penetration spot welds. These secure the components together without causing any change in the valve stroke setting, since the non-melted portions of the guide tube between the spot welds prevent dimensional change and absorb the shrinkage stresses. Thereafter, a continuous hermetic seam weld is made between the parts at a point axially spaced from the spot welds in a direction away from the valve seat. The spot welds then maintain the relative dimensions of the components between the spot welds and the valve seat so that any shrinkage in the assembly due to the seam weld occurs in the components away from the valve seat and has no effect upon the preset valve stroke.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.